If the checkbox is selected and there are entries from 5 days ago, what would be the correct action to take?

Also, what would cause them to not be deleted correctly?

For now I am running the following query against the Workflow database each night to keep it cleaned up until we figure out what is causing Workflow to not cleanup the tables correctly. Within a 24 hour period we are seeing over 400,000 rows in the table.

GO
DECLARE @counter AS INT = 1, @message AS VARCHAR(100)

WHILE EXISTS (
	SELECT 1
	FROM LF_Workflow.dbo.workflow_task_queue
	WHERE Status = 8
	)
BEGIN
	SET @message = 'Start of loop number ' + CAST(@counter AS VARCHAR) + ' - ' + CONVERT(VARCHAR(24), GETDATE(), 113)
	RAISERROR(@message, 10,1) WITH NOWAIT
	DELETE TOP (5000)
	FROM LF_Workflow.dbo.workflow_task_queue
	WHERE Status = 8
	SET @message = 'Completed loop number ' + CAST(@counter AS VARCHAR) + ' - ' + CONVERT(VARCHAR(24), GETDATE(), 113)
	RAISERROR(@message, 10,1) WITH NOWAIT
	SET @counter = @counter + 1
	WAITFOR DELAY '00:00:05'
END

We are experiencing the exact same thing.  One of our workflow servers suddenly decided that it wasn't going to clear the completed items in the workflow_task_queue table.  There were over 22 million entries.  The database kept growing and we didn't initially know why.

Also, if I uncheck "delete completed tasks based on a timer..." they are immediately deleted.  I do like the idea of only having one delete run every X minutes rather than a delete command every time an activity completes.  Did you ever figure out how to get this working again?  We even tried disabling/re-enabling, changing the values and then resetting them.  Nothing seems to matter.  No matter what we do, if we leave it set to delete on a schedule, it never runs.

Also, I couldn't find a SQL job or scheduled task that is triggered by this setting.  Do you know where the actual job lives?